Infection of susceptible chickens with cell-associated herpesvirus Marek's disease virus (MDV) results in a lymphoproliferative disease, characterized by development of visceral lymphomas composed predominantly of T lymphocytes. Although the mechanisms of viral oncogenesis in MD are not known, evidence suggests that the T cell may be the principal cell involved in the pathogenesis of the disease. In order to study the pathogenesic effects of MDV on T cells during the progressive development of acute MD, in vitro methods of cellular immunology will be applied. Cultures of T cells will be tested for mitogen responsiveness and functional reactivities in cell-mediated immunity (CMI). Immunofluorescent methods will be used to characterize tissue specific and virus-associated surface determinants of cultured lymphocytes. Cell separation procedures will be applied to obtain enriched populations, which may then be analyzed for immune reactivities or mixed wih normal cells to determine inhibitory or proliferative effects. Any alterations in functional reactivities and cell surface determinants will be assessed in terms of malignant transformation of the MDV infected lymphocytes. Similar tissue culture systems, using mitogens and IF methods, will enable the comparisons of cell populations derived from the transplantable MDT lymphoma and primary MD visceral lymphomas. Detection of similarities between malignant MDV-transformed lymphoma cells and cells in subpopulations of peripheral lymphoid tissues of MDV-infected chickens will be considered. The probable immunological basis for effective HVT vaccination against MD oncogenesis will be investigated in tissue culture systems, by comparing immune responses of lymphocytes from vaccinated and non-vaccinated chickens infected with MDV. These comparative studies may indicate the cellular effector of HVT protection. Finally, the possible role of humoral factors as mediators in pathogenesis of MD as well as in the HVT prophylaxis will be investigated. BIBLIOGRAPHIC REFERENCE: Effects of Lymphocytes from Marek's Disease-Infected Chickens on Mitogen Responses of Syngeneic Normal Chicken Spleen Cells. Gail A. Theis. J. Immunol. 118:887, 1977.